PEM vs Alkaline vs Solid Oxide Electrolyzers: The 2025 Hydrogen Technology Showdown
Alkaline electrolyzers use a liquid potassium hydroxide (KOH) electrolyte, operate at about 60–80 °C, and have decades of industrial use in chlor-alkali and fertilizer plants. PEM electrolyzers use a solid polymer membrane and typically operate at 50–80 °C, delivering very high-purity hydrogen (>99.999%), with iridium catalysts at the anode and platinum at the cathode. SOEC operate at 700–850 °C with a ceramic oxide-ion electrolyte, reduce steam to hydrogen, and can exceed 80% LHV electrical efficiency when heat is supplied, with Sunfire achieving about 84% LHV in a multi‑megawatt unit and NASA reporting a 4 MW SOEC system in 2023. CapEx
